AKD (alkyl or alkylketene dimer) is a kind of sizing agent for paper making. At present, the AKD products manufactured by industrial mass production are acquired by batch production. Along with the growth of market demand, this production method has major limitations and defects such as great quality fluctuation, high labor cost, high consumption of raw materials and energy, etc. Recently, the continuous preparation of AKD has become the development trend of large-scale mass production. Both European patent EP0550107 and Chinese patent CN1596252A disclose the methods for continuous preparation of AKD, but above-mentioned methods continuously feed all of raw materials acyl chloride and tertiary amine according to certain proportion for a single time, which causes the sudden rise of reaction temperature, sharp increase of material viscosity and difficult operation to fail to acquire the high purity products.
Chinese patent CN101845030A also discloses a kind of method for continuous preparation of AKD. This patent applies the specially designed reactor, with main body of conveyor carrying discontinuous propeller blades with fixed stirring rods inserted in the spacing of propeller blades. In two embodiments, one of raw materials tertiary amine is fed for a single time and the other raw material acyl chloride is fed for two times. And the product purity is greatly improved in comparison with control product. Although the iodine value of product could be stable at 43, the iodine value is about 2 less than that of products from batch production and the melting point is about 0.5˜10 C lower, which indicates that a lot of impurity exists, the product purity is not high enough and the product quality is not good; if the raw material acyl chloride is fed for three times, the product purity is not obviously improved due to limitation of reactor length, short reaction time and insufficient stirring especially during feeding of last batch of raw materials. The causes affecting the above-mentioned product quality are: (1) under the condition of being free from solvent, the reaction is very fast and even if one of materials acyl chloride is fed through two points, the heat of reaction is released quite concentratively and the reaction temperature is hard to control and the material viscosity is high; (2) this reactor relies on discontinuous propeller blade for shearing and kneading and its structure is simple and axial and radial mixing strength is low with poor self-cleaning capability, so that seizing and wall accretion might occur inside the reactor and the difficult heat dissipation causes the rising of reaction temperature and increasing material viscosity to result in insufficient mixture of materials and finally cause the insufficient dimerization reaction of acyl chloride and tertiary amine and failure of continuous preparation of high purity AKD products. Therefore, the topic of present invention is how to improve the process and device for realization of continuous preparation of high purity AKD products.